The INFORM HER2 dual in situ hybridization (DISH) DNA probe (Ventana Medical Systems, Tucson, AZ) cocktail assay is a technique designed to determine HER2 gene status by detecting HER2 copies via SISH and chromosome 17 (chromosome enumeration probe 17 or CEP17) copies via chromogenic red ISH on a single slide. An added advantage of these other ISH assays is the ability to analyze the tumor for HER2 heterogeneity more comprehensively. To overcome some of these limitations, the bright-field in situ hybridization (ISH) methods, such as chromogenic in situ hybridization (CISH) and silver in situ hybridization (SISH), were developed. Despite its usefulness, there are some limitations to the FISH assay, mainly related to dark-field fluorescence microscopy and lack of morphologic details. FISH has become universally accepted as a reference standard in the assessment of HER2 status and is often used to classify equivocal results by IHC. Most laboratories use IHC as a screening assay for all breast cancer cases and perform FISH testing on IHC 2+ cases. 6вЂ“8 The two US Food and Drug Administration (FDA)вЂ“approved methods in current clinical use to assess HER2 status in breast cancer are fluorescence in situ hybridization (FISH) to evaluate HER2 gene amplification and immunohistochemistry (IHC) to detect protein overexpression. Due to apparent heterogeneity of tumors, HER2 status should also be assessed on all recurrent and metastatic breast tumors. Therefore, HER2 status is determined on all newly diagnosed invasive breast carcinomas. 3вЂ“5 As a prognostic factor in breast cancer and a predictive factor for the effects of HER2-targeted drugs, HER2 assay is currently one of the most important tests for breast cancer. The clinical significance of ERBB2 ( HER2) gene 1 amplification in breast cancer was initially reported in 1987, 2 and since then the clinical experience has confirmed that approximately 15% to 20% of breast cancers demonstrate unequivocal HER2 gene amplification and/or protein overexpression.

Dual in situ hybridization stereology